1. Field of the Invention
The present invention relates to a low pass filter having an attenuation pole in a vicinity of a pass band, and a demultiplexer equipped therewith.
2. Description of the Related Art
In the past, as this type of low pass filter (hereinafter, referred to as a low pass filter (LPF) in some cases), for example, there has been a low pass filter described in Japanese Unexamined Patent Application Publication No. 2010-232765. This LPF includes a series arm, and, for example, three parallel arms. In this series arm, for example, two parallel resonant circuits are provided. A first parallel arm is provided between the input terminal of the LPF and a parallel resonant circuit located at a previous stage. In addition, a second parallel arm is provided between the two parallel resonant circuits. A third parallel arm is provided between a parallel resonant circuit located at a subsequent stage and the output terminal of the LPF. One capacitor is provided in each parallel arm.
In general, in accordance with requested specifications, the pass band, the frequency position of an attenuation pole, the size, and the like of an LPF are defined. However, when the LPF is miniaturized, in some cases it is difficult to mount a sufficient number of inductor elements or capacitor elements, and as a result, there has been a problem that it has been difficult to provide an attenuation pole in a desired frequency position.